The present invention relates to an electric brake actuator for actuating a brake arrangement. It will be convenient to describe the invention in relation to its application to the parking brake arrangement of a vehicle, although it is to be appreciated that the invention could have other applications, such as its actuating of brake arrangements in general.
Electric brake actuators have been considered in recent times as being attractive for parking brake actuation, by facilitating removal of the need for manual parking brake actuation by the vehicle driver and by providing greater control of the braking force which is applied. As yet however, an electric parking brake actuator that is generally acceptable to the automotive industry has not been provided.
It is an object of the present invention to provide an electric parking brake actuator for use in the automobile industry and which meets with general acceptance in that industry.
According to the present invention there is provided an electric parking brake actuator for actuating the parking brake arrangement of a vehicle, said actuator including an electric motor and a load multiplier, said electric motor being in cable connection through a first cable means (unit) with said load multiplier and said load multiplier being arranged for cable connection through a second cable means (unit) with said parking brake arrangement, whereby said electric motor is operable to apply a load to said load multiplier through said first cable means and said load multiplier is operable to multiply said load for application to said parking brake arrangement through said second cable means.
The present invention further provides a vehicle having an electric brake actuator for actuating the brake arrangement thereof, said actuator including an electric drive unit and a load multiplier, said electric drive unit being in cable connection through a first cable means with said load multiplier and said load multiplier being in cable connection through second cable means with said brake arrangement, whereby said electric drive unit is operable to apply a load to said load multiplier and said load multiplier is operable to multiply said load and apply said multiplied load to said brake arrangement, via said respective cable connections.
The above arrangement is advantageous because the load required to be applied by the actuator is significantly less than that applied to the parking brake arrangement. Because of this, the cable for driving the load multiplier can be relatively light grade compared to the cable extending from the load multiplier to the parking brake arrangement. Thus, the cable for driving the load multiplier can be relatively thin and flexible, which permits the load multiplier to be of reasonably small construction, so as to be unobtrusive where it is fixed to the vehicle. Additionally, being of light grade, the cable, if required, can be easily routed about the vehicle to which it is applied as necessary. Advantageously, this can permit the electric drive unit to be placed in an easily accessible position, such as within the cabin of the vehicle.
Accessibility is desirable, because preferably the parking brake arrangement is required to be manually operable in the event of failure of the electric drive unit or the power source supplying the electric drive unit and in that event, it is preferable that the driver of the vehicle can manually operate the electric drive unit, most preferably from the driver""s seat, because such failure will generally require the service brakes to be operated (normally foot operated) until such time as the parking brake arrangement can be manually applied.
Alternatively the electric drive unit could be located remote from the driver, but be manually actuable in the region of the driver""s seat. In this arrangement for example, the electric drive unit may be positioned adjacent the load multiplier and may even be connected to it or formed integrally with it, or it alternatively may be located in the engine bay. Regardless of the position of the electric drive unit, in this arrangement, an emergency or manual cable of light grade may be operable to manually actuate the parking brake arrangement through the load multiplier, either by bypassing the electric drive unit or by operating the drive unit manually. For example, the emergency cable may be an extension of the cable acted on by the electric drive unit, or in an alternative arrangement, it may be separately connected to the load multiplier, so as to actuate the load multiplier independently of the electric drive unit. The cable may have a handle at the free end thereof and because of the light grade of the cable, the cable can be easily routed so that the handle can conveniently be positioned for manual actuation, such as below the dashboard, or beneath the driver""s seat.
By the above arrangements, the load multiplier can also be placed in the most suitable position in the vehicle. That may also be within the vehicle cabin, but more likely, it will be outside of the cabin, such as fixed to the undercarriage toward the rear of the vehicle. Unlike the electric drive unit, the position of the load multiplier is preferably close to the rear axle, because the cable or cables extending between the load multiplier and the parking brake arrangement, which typically includes two parking brake assemblies operable on each of two rear wheels of a vehicle, is of relatively heavy grade, with limited flexibility for routing about the vehicle. Thus, a generally direct connection is required. However the present invention advantageously accommodates this requirement as the load multiplier can be positioned relatively close to the parking brake assemblies.
A load multiplier can take any suitable form and in a preferred form, it includes a plurality of pulley groups, a first of which is anchored against shifting movement, while a second group is movable toward and away from the first group. Each pulley group includes at least a single pulley, but preferably more than one. The electric drive unit can also take any suitable form and hereinafter it will be described as at least including an electric motor, although that is for convenience only. The electric drive unit could include a form of drive other than an electric motor and may include other components, such as control components, electrical supply components or supplemental load multiplier components.
The electric motor cable (hereinafter xe2x80x9cthe motor cablexe2x80x9d) threads or extends about the first and second pulley groups, while the parking brake arrangement cable or cables (hereinafter xe2x80x9cthe assembly cablesxe2x80x9d) extend from the second pulley group. The pulley or pulleys of each group may be mounted to rotate on an axle, the ends of which are connected to a yoke-like member to which cables can conveniently be attached. The number of pulleys in each group dictates the load multiplication applied to the assembly cable.
In a preferred arrangement, two assembly cables extend from the load multiplier, each extending to a separate parking brake assembly provided at each of two wheels of the vehicle. Alternatively a single cable may extend from the load multiplier for connection with a further cable arrangement that extends to each of the two parking brake assemblies.
The load multiplier can alternatively include an anchor to which one end of the motor cable is attached, while the pulley groups about which the motor cable extends are mounted to float linearly toward and away from each other. In this arrangement, a load applied to the motor cable can draw the pulley groups toward each other against biasing means biasing them apart and that movement can be transmitted either directly or indirectly to the assembly cables. This arrangement advantageously facilitates equal load being applied to each assembly cable as the pulley groups can float relative to one another against the biasing means. In this arrangement, each pulley group may be mounted on an axle as described above, the ends of which extend beyond each side of the respective pulley group and into engagement with a yoke-like member to which a cable connected to each parking brake assembly may extend.
In a further alternative arrangement, the load multiplier includes a second pulley group or pair of pulley groups disposed between the first pair of pulley groups and diverting the path of the motor cable within the load multiplier. In this arrangement, assembly cables can be fixed to each of the first pulley groups, while the opposite ends of the motor cable which extends about each of the first pair of pulley groups and the or each of the second pulley groups, may be attached respectively to the electric motor and a manual actuator. By this arrangement, a load can be applied to the assembly pulley groups by either the electric motor, or by manual actuation. Advantageously, the second pair of pulley groups can be arranged to guide the motor cable in such a manner that the assembly cables extend from the load multiplier in an appropriate direction. In a preferred arrangement, the second pair of pulley groups is laterally offset different amounts along a centre-line between the first pair of pulleys in substantially the same plane as the cable path between the first pair of pulley groups.
In an electric actuator according to the invention, a second load multiplier may be employed and in one preferred arrangement, the second load multiplier is spaced from the first load multiplier, such as at or closer to the electric drive unit. That load multiplier can also take any suitable form and in this respect, either load multiplier can be of the form described above, or alternatively it could be of a different form, such as a screw and nut form or, a worm and wheel form. In this arrangement, the load multiplication provided may be split either equally or unequally between the first and second load multipliers and the use of two load multipliers may facilitate smaller componentry, greater load multiplication, or more flexible layout of components.